1. Field of the Invention
Production of complicated components from metallic or ceramic materials, the starting materials used being powders. Questions of sintering and hot-isostatic pressing with regard to the shrinkage.
The invention relates to the further development, perfection and simplification of powder-metallurgical fabrication methods for the production of workpieces having comparatively complicated shapes, where the problems of shrinkage during sintering play an important part. The field of application is especially the sector of turbine engineering components.
In the narrower sense, the invention relates to a process for the powder-metallurgical production of a workpiece, utilizing a sintering process in which a powder or powder mixture is first filled into a mold and mechanically precompacted by tapping, jolting or vibration.
2. Discussion of Background
Numerous fabrication methods in the metallurgical and ceramic industry start from powders. Powder-metallurgical processes have the advantage that virtually any desired shape can be obtained. It is intended to produce workpieces as finished components by powder metallurgy, in order to be able partially or wholly to save expensive machining costs. The known processes for achieving net shapes or near-net shapes of the workpieces all start from suspensions (slip, paste) of powders in solvents, using a binder. The following are used as additives to powder mixtures:
Water+binder+additives (slip casting, freeze drying)
Water+cellulose (metal powder injection-molding according to Rivers: MIM by Rivers process)
Thermoplastics (metal powder injection-molding)
In all these wet-mechanical methods, numerous difficulties arise with respect to quality, freedom of design, reproducibility and selection of the composition:
Bubble formation on mixing of powder with binder and solvent.
Limitation of the wall thickness of the workpieces (for example at most 5-10 mm for MIM) since otherwise the binder can no longer be completely removed.
Appearance of binder residues (for example carbon) which remain in the workpiece even after the binder has been "burned out" and can impair the composition of the workpiece in an uncontrolled fashion.
Necessity of new selection/new development of the binder when changing over to other shapes and/or compositions of the workpieces.
Regarding the state of the art, the following printed publications are cited:
British Patent Application 2,088,414
European Patent Application 0,191,409
R. Billet, "PLASTIC METALS: From fiction to reality with injection-molded P/M materials", Parmatech Corporation, San Rafael, CA, P/M-82 in Europe Int. PM-Conf. Florence I 1982.
E. Lange and M. Poniatowski, "Pulvermetallurgisches Spritzgiessen - ein neues Formgebungsverfahren fur Sinterteile komplizierter Gestalt [Powder-metallurgical injection-molding--a new shaping process for sintered components of complicated shape]", Konstruktion 40 (1988) 233-238
Goran Sjoberg, "Powder Casting and Metal Injection Moulding", manuscript submitted to Metal Powder Report September 1987
The known processes leave something to be desired. There is therefore a demand for improvement and further development of the powder-metallurgical/powder-ceramic fabrication methods.